An engine bearing of this type has been known from, e.g., DE 36 14 161. In the two-chamber step bearing disclosed in this document, the working chamber and the compensating chamber are provided with walls consisting of ring-shaped rubber membranes, which have a predetermined buckling characteristic adapted to the operating load.
The compensating chamber and the working chamber are connected to one another by a nozzle chamber, whose walls are formed by corresponding profiles overlapping one another in two rigid components adjustable in relation to one another, wherein the two components are axially adjustable in relation to one another by means of a screwable adjusting member, which is mounted coaxially to the principal axis of the bearing and is fixed in the axial direction in the bearing housing of the two-chamber step bearing and can be actuated by means of a component projecting from the housing.
The adjustment of the nozzle channel cross section is performed by means of a spindle, which is mounted freely rotatably in the bearing housing, wherein one of the two components forming the nozzle channel is in threaded engagement with the spindle for the axial adjustment, so that a reduction or enlargement of the nozzle channel cross section can be brought about by rotating the spindle.
Even though a certain adjustment of the two-chamber step bearing to the design requirements of the engine, whose vibrations are to be damped by the bearing, is possible due to the exclusively manual adjustability of the two-chamber step bearing by means of the component projecting from the housing, adjustment during the running operation is ruled out because of the existing installation conditions.
Moreover, an additional stiffness of the fluid cushion in the working chamber, which is desirable because of different operating states, is not possible in the two-chamber step bearing disclosed in the above-mentioned document. However, precisely the combination of influencing both the nozzle cross section and the damping capacity of the hydraulic cushion within the working chamber would make possible a much better adaptation of the two-chamber step bearing to the different operating conditions of the engines to be mounted within motor vehicles. Such an adaptation is required especially in the case of the use of direct injection diesel engines, which are frequently used now, and whose vibration characteristics are determined by different vibration characteristics at idle and during travel with different vibration frequencies far more greatly than in the case of the gasoline and diesel engines that have been used hitherto.
In the two-chamber step bearing known from the state of the art, an increase in the channel cross section leads to an increase in the damping of the bearing, without a change in the frequency level or the dynamic stiffness of the bearing. This increase in damping is quite important for the elimination of low-frequency high-amplitude vibrations.
However, the additionally occurring high-frequency vibrations with small amplitudes can be effectively controlled only by changing the stiffness of the ring-shaped rubber membrane or of the fluid cushion cooperating with same.